Hurricane forecasters are reporting signs of a developing El Niño, a weather phenomenon that can significantly suppress the number of hurricanes over the upcoming six-month Atlantic season.
"Most of the models right now are forecasting it," hurricane forecaster Phil Klotzbach said.
El Niño would be the key factor in determining hurricane activity during the season, which runs from June 1 through Nov. 30.
An El Niño occurs when warm surface waters from the western Pacific Ocean are pushed to the eastern Pacific. The warmer surface waters cause upper-atmospheric storms and shearing winds that can thwart hurricane formation thousands of miles away in the Atlantic basin — the Gulf of Mexico, Caribbean Sea and Atlantic Ocean.
Warmer surface waters are being measured by ships, buoys and satellite technology but still need a stronger push, experts say.
"We've been seeing strong westerly winds near the international date line for a few weeks, and that's usually a pretty good precursor of an El Niño event," Klotzbach said.
Preliminary signs show potential for a strong El Niño, possibly during peak hurricane season in late summer, said Jeff Masters, director of meteorology for Weather Underground.
"What we are seeing is similar to 1997, before the start of the greatest El Niño ever recorded," Masters said.
In the 1997 El Niño, it was a typhoon east of the Philippine Islands that created a burst of westerly winds, pushing the warm surface water to the east, Masters said. Only nine storms formed that year, three of them hurricanes.
El Niños, which generally occur every two to seven years, have been traced back tens of thousands of years and are considered part of the basic cycle of the Pacific Ocean. A La Niña is the opposite of El Niño, in which warm surface waters slough back to the western Pacific.
An El Niño can increase surface water temperatures a degree or two or, in extreme cases, as much as 5 or 6 degrees in areas of the eastern Pacific, especially near the equator. Such a change, even when modest, can stoke the atmosphere, causing the type of storms that can disrupt hurricane formation or push storms away from the U.S.
The National Center for Climate Prediction on Thursday issued an El Niño watch: a greater than 50 percent chance of an El Niño in the next three to six months.
At least one other key factor in hurricane formation is pointing to a possible slowdown in seasonal activity: Sea surface temperatures are slightly below normal.
"The Atlantic right now is cooler than normal, maybe just a half-degree or so, but that's significant," said Klotzbach, who, along with veteran hurricane forecaster William Gray, will issue annual seasonal predictions in early April.
The reality is that neither El Niño nor cooler sea surface temperatures are a guarantee against disaster.
Some of the most destructive storms in history occurred during El Niño years. In 2004, four strong hurricanes hit Florida in what was considered a weak El Niño.
And forecasters acknowledge that early season forecasts are not always spot-on.
Most major forecasters badly erred in last year's seasonal projections, predicting on average about 17 named storms, half of them hurricanes and half of those major hurricanes with winds of 130 mph or more.
The season produced only two hurricanes. Neither of them were major storms.
What's more, accumulated cyclonic energy — a measure of the total amount of tropical energy in the Atlantic basin — was about a fourth of the norm.